The photoredox reactions of biologically important phenols (p-coumaric acid, ferulic acid, thymol, quercetin and gallic acid) with the excited state *[Ru(nbpy)3]2+ (nbpy = 4,4'-dinonyl-2,2'- bipyridine) complex proceeds through photoinduced electron transfer reaction in 50 % aqueous acetonitrile at pH 11 and has been studied by luminescent quenching technique. The complex shows absorption and emission maximum at 456 and 618 nm and it shows a life time at 625 ns in 50 % aqueous acetonitrile at pH 11. The dynamic nature of quenching is confirmed from the ground state absorption studies. The reductive quenching of [Ru(nbpy)3]2+ by the phenolate ions have been confirmed from the transient absorption spectra. The quenching rate constant, (kq) is highly sensitive to the availability of active phenolate ions, oxidation potentials of the phenols, the free energy change, (DG0) of the reaction and the electron transfer distance between the donor and the acceptor